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KITTTTAS COUNTY <br />DEPARTMENT OF PUBLIC WORKS <br />STUDY SESSION STAFF REPORT <br />STUDY SESSION DATE: October 23, 2017 <br />ACTION REQUESTED: Request to approve a Resolution for the removal of <br />the Bar 14 Road Bridge over Naneum Creek and to <br />perform channel grading in the vicinity of the bridge. <br />BACKGROUND: The Bar 14 Bridge over Naneurn Creek suffered <br />significant damage during the flood events in the <br />spring of 2017 and can no longer be maintained at a <br />full service level. Flooding caused debris to build up <br />under the bridge, completely blocking flow <br />underneath the bridge. Water was forced to route <br />around the bridge on either side, washing out the <br />approach roadway. <br />This bridge has historically had issues with debris <br />buildup, and Public Works has had to dredge the <br />creek under the bridge annually for many years. <br />After flooding subsided and Public Works was able <br />to dredge out debris from under the bridge, it was <br />discovered that the northernmost girder suffered <br />significant damage, severely reducing its load <br />carrymg capacity. The bridge was analyzed by <br />structural engineers from the consultant firm KPFF, <br />who recommended the bridge be opened to a single <br />lane configuration to keep traffic off of the damaged <br />girder. <br />Public Works then began working toward a plan to <br />replace the bridge. In doing so, hydraulics engineers <br />from Consultant firm NHC were brought in who <br />specialized in geomorphology and sediment <br />transport. They visited the site and walked the creek <br />channel upstream and, downstream with Public <br />Works personnel to determine the root cause of the <br />debris buildup at the bridge. <br />It appears that the irrigation structure downstream, <br />where Naneum Creek intersects the Hiline Canal, has <br />prevented bedload from moving downstream and as <br />